Voltage biasing of magnetic amplifiers



Nov. 26, 1957 R. D. TORREY 2,314,734

VOLTAGE smsmc OF MAGNETIC AMPLIFIERS Filed June 7, 1956 MM'ig-l; FIG. 2.

D3/ RI RL l6 Blocking Pu Source FIG. 3.

A Power Pulses l INVENTOR ROBERT D TORREY A GENT B. Blocking Pulses United States Patent VOLTAGE BIASING on MAGNETIC AMPLIFIERS Robert D. Torrey, Philadelphia, Pa., assignor to Sperry Rand Corporation, New York, N. Y., a corporation of Delaware Application June 7, 1956, Serial No. 590,016

15 Claims. (Cl. 307-88) The present invention relates to improved magnetic amplifiers primarily of the type exhibiting ringback efiects; and is particularly concerned with improved biasing arrangements for suppressing undesired current flow in the input circuit of such a magnetic amplifier, due to ringback compensation. In this respect, the present invention comprises a continuation-in-part of the prior copending application of Robert D. Torrey et al., Serial No. 499,905, filed April 7, 1955, for: Magnetic Amplifier.

As has been discussed in the aforementioned prior copending application, magnetic amplifiers of the type contemplated herein may be of either the series or parallel types, and may take a number of configurations whereby complementing or non-complementing operation is effected. In this respect, a complementing amplifier is defined as one which normally produces outputs in the absence of inputs thereto, and wherein inputs tend to inhibit outputs; while a non-complementing amplifier is defined as one producing an output only in response to the application of an input thereto.

Amplifiers of these general types normally comprise a core of magnetic material which may exhibit a substantially rectangular hysteresis loop, or which may in the alternative exhibit other hysteretic configurations; and such a core normally carries a power winding and an input winding thereon. In the case of series type amplifiers, the power winding may also comprise the output winding of the system; while in the case of parallel type amplifiers, a further winding may, if desired, serve as the output winding. In either case, however, it is customary to energize the said power winding by a source of spaced regularly occurring power pulses which may be of rectangular, sinusoidal, or of other alternating configuration; and rectifier means are normally disposed in series with the said power winding and with the said power pulse source, whereby pulses of a preselected polarity efiect current flow through the said power winding in a desired direction. This desired current flow may selectively cause the aforementioned core to traverse either a saturated or an unsaturated portion of its hysteresis loop, in dependence upon signals applied to the aforementioned input winding, whereby outputs selectively appear or are absent in accordance with the particular hysteretic portion of the core being traversed. In the a case of series type magnetic amplifiers, for instance, an

occurrence of ringback current in the said power winding .subsequent to cessation of a given power pulse and prior tooccurrenCe of a next subsequent power pulse. ringback currents may 'occurfor a number of reasons,

Such

and are primarily caused by the inductance and distributed capacity of the power winding as well as by back current flow and possible transient enhancement current flow through rectifiers placed in series with the said power winding and the said power pulse source.

The characteristics of such ringback current will become more readily apparent from the subsequent description, but for purposes of that description, as well as of the appended claims, ringback current is defined as a transient current flowing in the amplifier power winding in a direction opposite to that efiiected by operative power pulses coupled to said power winding, and occurring at times intermediate the occurrence of said operative power pulses. The aforementioned ringback currents, being in a direction opposite to the operative power pulses, tend to reset the core from a desired remanence point on the major hysteresis loop of the core material to an undesired remanence point on a minor hysteresis loop of the material, whereby a next subsequent power pulse must drive the core through an unsaturated portion of its hysteresis loop prior to the production of an output from the amplifier. This consideration, of course, reduces the amplitude of output from the amplifier and results in a decreased efiiciency of operation.

The aforementioned prior copending application Serial No. 499,905 discusses a number of circuits serving to compensate for ringback current, and these circuits in general take the form of a bias source operative intermediate the application of power pulses to reset the core from an undesired operating point, to which it has been driven by ringback current, back to a desired operating point preparatory to application of a next subsequent power pulse. It will be appreciated that this resetting of the core, to compensate for ringback, produces flux changes within the said core which may in turn induce an undesired potential in the amplifier input winding; and the present invention is primarily concerned with the suppression of undesired current flow in the said input winding due to the aforementioned resetting of the core in compensation for ringback. It will be understood that although a single embodiment operative in this manner will be described hereinafter, the invention finds equal applicability to the several amplifier circuits discussed previously, as Well as to the various ringback compensation circuits shown in the said prior copending application Serial No. 499,905.

It is accordingly an object of the present invention to provide an improved magnetic amplifier circuit.

Another object of the present invention resides in the provision of a magnetic amplifier circuit compensating for ringback in a more efiicient manner than has been the case heretofore.

A still further object of the present invention resides in the provision of novel biasmeans for use in a magnetic amplifier circuit whereby current flow in the input circuit, due to ringback compensation, is inhibited.

A still further object of the present invention resides in the provision of a magnetic amplifier having improved power gain.

A further object of the present invention resides in the provision of means avoiding undesired loading of an input source, due to undesired current flow in the input winding of a magnetic amplifier.

The foregoing objects, advantages, construction and operation of the present invention will become more readily apparent from the following description and accompanying drawings, in which:

Figure 1 is a hysteresis loop of a magnetic material which may preferably but not necessarily be employed in the cores of magnetic amplifiers utilized in accordance with the present invention.

Figure 2 is a schematic diagram of one form of mag- .number of structural configurations.

ciples to be discussed vare equally applicable .to other forms of magnetic amplifiers both of the pulse and carrier types. The core preferably, but not necessarily, comprises a magnetic materialexhibiting a substantially rectangular hysteresisloop, and the-said core may assume a Itshould be noted, however, that the,present invention is not limited to any specific structural or hysteretic configuration for the core, and various alternativesin this respect will be obvious-to those skilled inthe art.

Power winding-11 is coupledat its upper end via rectifier D1 to asource13'of regularly. occurring positive and negative going powder-pulses (Figure 3A), and as men tioned previously, these pulses may-in fact assume a number of possible alternating configurations. The lower end .ofwinding 11 is coupled via-rectifier D2 to an output point.14 whereby outputs may be selectively taken across aload R and a clamp or sneak suppressor circuit D3-R1is also coupledzto thesaid power winding 11, whereby only desired pulse outputs appear at the terminal 14. .Signal or input winding 12 is coupled at its upperend viarectifier D4 to an input terminal 15, and is further coupled at its lower end to ablocking pulse source 16 producing regularly occurring pulses of the 'type illustrated in Figure 3B.

Asmentioned previously, the circuit shownin Figure 2 exhibits complementing operation-in that "outputsrare achieved in the absence ofinputsthereto, while the application of an input inhibitsan;output.

Thev theoretical operation of thecircuit istasjlfollowsz If we should initially assume that the, core -10 is atrits ;plus'. remanence. point (Figure-1),Lthe-application :ofra; positive going :power pulse .at terminal-13,;during a. time .intervalri t1 to 12,- will -efl:'ect current*flowzthroughopower winding 11*whereby pedance and substantially allthe'energy ,of=the -power pulse is coupled via rectifier .D,1,- winding-11, and rectifier D2 to the output point 14. During: this same time interval II to 12, the blockingpulsesource: 16 rises: to a POSIUVC potential +132 at the lower endof-input winding 12 thereby to assure that rectifier. D4 isJdisconnected so that the aforementionedqflux' changes in core .10 do not eifectcurrent flow. in input winding. 12. So long as no input pulses are applied at terminal 15, therefore, the core 10 is regularly driven from plus remanence point 20 to positive saturation-regiomZl; and each positive going power pulse therefore effects .a pulse output at'terminal 14.

Upon application of anLinput pulse at terminal 15, during a time interval when thepowertpulsesat terminal 13 are negative; going. (for instance duringtimeinterval t2 to 13), current flow is etfectedu-in the input winding 12 whereby the core 10 isnswitched from 'itsplus remanence operating point20-to the beginning 22 of the .negative saturation region;-andupon removal of =the .said

. input signal, the said core moves to. negative remanence .puts are desired from the amplifier. .ever, deviations from this theoretical operation occur,

13 to 4, drives the core through an unsaturated region from negativeremanence point 23 to the beginning 24 of the positive saturation region. For operation in this unsaturated region of the core, a relatively large flux change occurs in core 10 whereby winding 11 exhibits a high impedance to the applied positive going power pulse, and substantially all the energy of the said power pulse is absorbed in winding 11. The small sneak output which might in fact occur during operation between points 23 and 24 is absorbed by sneak suppressor D3-R1. in the absence of a further input pulse, the core 10 will return to positive remanence operating point 20 whereupon the next subsequent positive going power pulse again drives the core into positive saturation to effect an output from the amplifier.

It will be appreciated that for the theoretical operation discussed above, core 10 should be driven between points 20 and 21 by each positive going power pulse when out- In practice, howpulse at terminal 13 falls to a negative potential, and

under such conditions of operation the core should theoretically return to positive remanence operating point 20. The inductance 19 and distributed capacitance 17 of output winding 11, however, tends to effect a current fiow through the winding 11 in a direction opposite to that effected by positive going power pulses when the said power pulses fall to a negative potential. This reverse current flow is further aggravated by possible leakage in a back direction through rectifier D1 via the equivalent leakage resistance 18 when terminal 13 goes negative, as well as by transient-enhancement or charge storage current which may be effected in a reverse direction through the said rectifier D1, if rectifier D1 (or rectifier D2 for that matterlcomprises a semiconductor material.

The combined effect of the inductance 19 and distributed capacity 17 of power. winding 11, in combination with back'leakage resistance 18 and enhancement current flow through rectifiers which may be employed in the circuit, is, to produce a pulse of current through winding 11 in a direction opposite to that effected by positive going powerpulses, and occurring at a time immediately subse- 13, therefore, must drive the core 10 throughan unsaturated portion of its hysteresisyloop before an output is achieved, wherebydecreased efficiency of operation is eifected.

The aforementioned copending application SerialNo. 499,905 relates to a number of circuits overcoming the undesired effect of ringback current whereby the efiiciency of the amplifier is increased, and such circuits may include a separate bias-winding on core 10 for ringback compensation; or'may, in the alternative, comprise a bias source coupled to either "the input or output winding'of the amplifier. A typical such ringback compensation circuit may comprise a bias current source which includes resistor R2 and potential source +V2 coupled to power winding 11 in the manner illustrated in Figure 2. In operation, the bias source comprising elements +V2, and R2, 75,

effects a bias current flow through winding 11 in a -direction opposite to that effected by the aforementioned ringback currents whereby the core 10, which has been driven to operating point 26 by ringback currents, is returned to operating point 20 prior to occurrence of a next subsequent power pulse.

While the aforementioned ringback compensation circuits do overcome the ringback effects mentioned, their operation is accompanied by a further disadvantage. It will be noted that the operation of the ringback compensator circuit is such that core is moved from an operating point, such as 25 or 26, back to operating point 20 intermediate the application of the aforementioned spaced positive going power pulses. During this resetting of the core from point 26 to point 20, a small flux change occurs in the core 10 in a direction the same as that effected by positive going power pulses applied to the power winding 11. This small flux change occurring during ringback compensation, therefore, tends to induce a potential in input winding 12; and inasmuch as the blocking pulse source 16 would, in normal practice, return to a ground potential level intermediate positive going power pulses, this induced potential in input winding 12 may effect an undesired current How in the input circuit, thus imposing a larger bias current requirement on the circuit.

In accordance with the present invention, therefore, further bias means are provided for inhibiting such undesired current flow in the input circuit during ringback compensation, and such further bias means may again comprise the blocking pulse source 16 so modified that the source continues to exhibit a small positive potential +E1 intermediate the application of positive going power pulses to the circuit, and at times when ringback current and ringback compensation may be taking place. The potential level +E1 is so selected that it is substantially equal to and of opposite polarity to any potentials which might be induced in input winding 12 during the aforementioned ringback compensation whereby undesired current flow, due to ringback compensation flux changes, is avoided in the input winding 12.

While I have described a preferred embodiment of the present invention, many variations will be suggested to those skilled in the art. In particular, it must be emphasized that both the input bias source and the input blocking source discussed may comprise a pulse source or may be steady state in nature. In addition, the input bias source finds ready utility in magnetic amplifier circuits of various types wherein ringback compensation is to be efiected; and in particular, the invention should not be considered as limited to complementing amplifiers, to pulse type amplifiers, or to amplifiers of the series type, but may in fact be utilized in conjunction with the several forms of amplifiers discussed above, as well as with the various other forms of ringback compensators. The foregoing description is, therefore, meant to be illustrative only and should not be considered limitative of my in- Vention, and all such variations as are in accord with the principles discussed are meant to fall within the scope of the appended claims.

Having thus described my invention, I claim:

1. A magnetic amplifier comprising a core of magnetic material having first and second windings thereon, a source of selective signals coupled to said first winding, a source of spaced power pulses coupled to said second winding whereby a selected one of said power pulses drives said core between a first hysteretic operating point and a second operating point in response to a preselected signal state at said first winding, said selected power pulse tending to ettect a transient current in said first winding subsequent to cessation of said selected power pulse thereby to drive said core to a third hysteretic operating point, first bias means coupled to said amplifier for returning said core from said third hysteretic operating point to said first hysteretic operating point prior to occurrence of a next subsequent power pulse, and second bias means coupled to said amplifier for inhibiting current flow in said first winding due to flux changes in said core during return of said core from said third operating point to said first operating point.

2. The combination of claim 1 wherein said first bias means is coupled to said second winding, said second bias means being coupled to said first winding.

3. The combination of claim 1 wherein said second bias means comprises a blocking pulse source having a first potential level during occurrence of said power pulses and a second potential level intermediate said power pulses, whereby said blocking pulse source inhibits current flow in said first winding due to flux changes in said core during movement of said core between both said first and second operating points and between said third and first operating points.

4. A magnetic amplifier comprising a core of magnetic material having a power winding and an input winding thereon, a source of spaced power pulses coupled to said power winding, means for selectively applying input signals to said input winding intermediate selected ones of said spaced power pulses, said selected power pulses ef fecting ringback current in said power winding at times intermediate the occurrence of said power pulses whereby said ringback current sets said core to an undesired hysteretic operating point, means operative intermediate said power pulses to reset said core from said undesired hysteretic operating point to a desired hysteretic operating point, and bias means coupled to said input winding for inhibiting current flow in said input winding due to flux changes effected by the said resetting of said core to said desired operating point.

5. The combination of claim 4 wherein said bias means comprises a source of spaced blocking pulses coupled to said input winding.

6. The combination of claim 5 wherein said spaced power pulses are positive going in polarity, said blocking pulses being positive going substantially in coincidence with said positive going power pulses, said blocking pulses having a positive potential level with respect to ground potential intermediate the positive going excursions thereof.

7. A magnetic amplifier comprising a core of magnetic material having a power winding and an input winding thereon, a source of alternately positive and negative going power pulses, means coupling said source to said power winding, rectifier means in series with said source and said power Winding whereby power pulses of a preselected polarity are operative to effect current flow in said power winding in a first direction thereby to efiiect desired flux changes in said core, said power pulses eifecting transient current fiow in said power winding in a second direction opposite to said first direction during occurrence of power pulses having a polarity opposite to said preselected polarity, said transient current flow serving to set said core to an undesired hysteretic operating point, control means coupled to said amplifier for resetting said core from said undesired operating point to a desired operating point whereby undesired flux changes are effected in said core during said core resetting, and bias means coupled to said amplifier for inhibiting current flow in said input winding due to said undesired flux changes.

8. The combination of claim 7 wherein said control means includes further bias means comprising a current source coupled to said power winding.

9. The combination of claim 8 wherein said first mentioned bias means comprises a voltage source coupled to said input winding.

10. The combination of claim 9 wherein said voltage source is pulsating in nature.

11. A magnetic amplifier comprising a core of magnetic material having a power winding and an input winding thereon, means effecting desired current flow in a first direction through said power winding during spaced time intervals said desired current flow through said power winding eifecting undesired current flow in a Second direction opposite to said first direction through said power winding at times intermediate said spaced time intervals whereby said undesired current flow drives said 4 9 war f .3 i i hystcl'fitic p l P means for resetting said core to said desired hysteretic operating point, and means coupled to said input winding for inhibiting current flow in said input winding due to flux changes effected by said resetting of said core.

12. The combination of claim 11 wherein said means effecting desired current flow comprises a source of spaced power pulses coupled to one end of said power winding, and load means coupled to the other end of said power winding.

13. A magnetic amplifier comprising a core of magn etic material having a power winding and an input winding thereon, power pulse means selectively eifecting undesired transient current flow in said power winding whereby said core is moved from a desired hysteretic operating point to an undesired hysteretic operating point, first bias means coupled to said amplifier for resetting said core from said undesired operating point back to said desired operating point, said input winding having an undesired potential induced therein due to flux changes in said core during said resetting operation, and second bias means for inhibiting current flow in said input winding due to said undesired potential induced therein.

14. The combination of claim 13 wherein said first bias means comprises a. current source coupled to said power winding for effecting current flow in said power winding in a direction opposite to said undesired transient current flow.

15. The combination of claim 13 wherein said second bias means comprises a potential source coupled to said input winding and having a bias potential opposite in polarity to that of said undesired induced potential.

No references cited. 

